LED blinking red usually means the battery has been completely dry (empty). If this is the case, you should actually let the phone charge the battery until the LED turns green. Don’t switch it on before.
The usual succession of LED colours should be: Blinking red (if the battery was all dry), constant red, yellowish and finally green when it is above 90 or 95%, see
If you don’t know yet: Don’t let the battery run all dry, see